At Damen’s Research and Development department, continuous improvements are made to existing design practices using recent technological developments and fatigue design is currently on the anvil. High speed craft operating around the globe are subject to millions of load cycles (resulting from ocean waves) and therefore suffer from metal fatigue. As per current practice, such vessels are designed for fatigue using inhouse software with a nominal stress approach supported by static sea-state scatter data and judgement based operational profiles.
Recently, new data sources with real time sea-state data over the whole globe have come available, including GPS locations of ships. Together, this enables it to generate real time operational profiles for its ships. A total stress concept has been developed based on results from a JIP called VOMAS. This approach has shown to provide accurate fatigue lifetime estimates for arc-welded aluminium joints. Similar results are expected for steel joints as well.
The main goal of this thesis was to explore possible improvements for the fatigue design methodology. A tool called Tanaav was developed for this purpose which makes use of both remote monitoring data and the total stress concept and provides an estimate of the yearly fatigue damage and fatigue lifetime. The tool has been used to predict the fatigue lifetime for three fatigue sensitive details in 46 FCS5009 vessels. Results have been compared to corresponding predictions using current and past fatigue analysis practices. It was observed that using both remote monitoring data as well as the total stress concept provides significant improvements in the predicted fatigue life time.
Uncertainties in fatigue influence parameters affecting the predicted fatigue damage can be incorporated using probabilistic. This thesis proposes a method for this and presents two cases as a proof of concept. Work done in this thesis will be validated by Damen in future with the help of full-scale testing on an actual FCS5009 vessel during an offshore measurement campaign. After validation, this method will help in improving fatigue design practice, increasing design flexibility and in optimizing vessel weights in a responsible way.